Method for the manufacturing high-temperature resistant engine components

ABSTRACT

For near net shape manufacturing of high-temperature resistant engine components of geometrically complex design consisting of an intermetallic phase, a low melting-point metallic phase in the molten state or in a temperature range near the molten state is mixed with a high melting-point metallic phase provided as a metal powder, and the mixture is mechanically treated under the effect of kneading and shear forces, thereby heating it up and reducing its viscosity. In a subsequent injection moulding process the engine component substantially matching the final contour is formed and mechanically finish-machined, if required, and afterwards subjected to a heat treatment for creating an intermetallic phase.

This invention relates to a method for near net shape manufacturing ofengine components of geometrically complex design consisting of anintermetallic phase.

It is generally known to manufacture components of geometrically complexdesign in a few working steps and in near net shape by metal injectionmoulding. In metal injection moulding (MIM), first a metal powder ismixed with a binder including thermoplastics and waxes to form a flowingmaterial (feedstock). The material in granulate form is injected into amould using an extruder in a conventional injection moulding process.After cooling, solidification and demoulding, a so-called green compactis initially created, from which the binder is then removed chemically,thermally or catalytically. The porous brown compact resulting fromdebindering is compacted into its final form in a subsequent sinteringprocess and has, due to its minor residual porosity, mechanicalproperties substantially matching the properties of the solid material.

For near net shape production of high-temperature resistant components,super-alloys provided in powder form are processed in the MIM method, asis well known. Furthermore, the proposal has already been made toproduce a metal powder consisting of an intermetallic phase and tomanufacture from this, on the basis of metal injection moulding,high-temperature resistant engine components near to their finaldimensions and with a metal-cutting expenditure that is reduced whencompared with conventional manufacturing methods. Conventionalmanufacture of intermetallic phases and of a metal powder made therefromfor metal injection moulding involves high effort and costs in addition,near net shape and dimensionally accurate production of the componentpresents problems due to the shrinkage of the brown compact as a resultof the sintering process following debindering.

The object underlying the present invention is to provide a method forcost-efficient near net shape manufacturing of high-temperatureresistant engine components of geometrically complex structureconsisting of an intermetallic phase.

It is a particular object of the present invention to provide solutionto the above problematics by a method in accordance with the features ofpatent claim 1.

Advantageous developments of the present invention become apparent fromthe sub-claims.

The basic idea of the invention is to use metal injection moulding tomanufacture engine components consisting of an intermetallic phase,where however a low melting-point metallic phase in the molten ornear-molten state is used as the binder and the metal powder is madefrom a higher melting-point metallic phase, and the moulded partobtained as the result of an injection moulding process andsubstantially matching the final contour does not have the binderremoved, but instead is subjected to a heat treatment for creating anintermetallic phase. As a result, it is possible with a low productioneffort and low cost expenditure to manufacture near net shape andhigh-temperature resistant engine components consisting of anintermetallic phase and having a geometrically complex structure. Withthe same method, three or more metallic phases can also be used tomanufacture high-temperature resistant engine components consisting ofan intermetallic phase.

Mixing of the low melting-point phase in the molten or near-molten statewith the metal powder consisting of the high melting-point phase isperformed in an extruder under the effect of kneading and shear forcesgenerated by an extruder screw. The result is very thorough mixing and atemperature increase, plus a reduction in the viscosity of the metalpowder/melt mixture for performance of the injection moulding process.

In a further embodiment of the invention, the metal powder/melt mixturecan be additionally heated in the extruder by heating means.

The engine component demoulded after solidification can be subjected toa finish-machining process before the heat treatment.

An exemplary embodiment of the invention is explained in more detail onthe basis of the drawing, the sole figure of which shows schematically ametal injection moulding device, and on the basis of a processing flowchart.

In step I of the method for near net shape manufacture of ageometrically complex and high-temperature resistant engine componentconsisting of an intermetallic phase, for example of a turbine blade, afirst low melting-point phase, for example aluminum, is provided in themolten state, and a second high melting-point metallic phase, forexample iron, is provided as the metal powder. The first lowmelting-point metallic phase can also be provided in a not completelymolten state, in the case of the aluminum used here, in a temperaturerange between 400° C. and 600° C. below its melting point. Compared witha metal powder consisting of an intermetallic compound, the metal powdermade from a metallic phase (in this case iron) can be manufactured withlow expenditure.

In the subsequent step II, the molten low melting-point metallic phase(aluminum) and the high melting-point metallic phase (iron) provided asa metal powder are filled into an extruder 3 using a first and secondhopper 1, 2 respectively. In step III, which takes place inside theextruder 3, the two metallic phases are intensively mixed with oneanother. Due to the shear and kneading forces exerted by the extruderscrew 4 onto the mixture, the viscosity of the mixture furtherdecreases. Due to the mechanical force effect and possibly the extruderheater, the mixture is also heated.

The mixture of a powdery high melting-point metallic phase and a lowmelting-point molten metallic phase (Fe, Al), previously transformedinto a low-viscosity and injectable state, is now introduced byinjection moulding into a mould 5 in step IV. Unlike in a conventionalmetal injection moulding method, the binder necessary for the injectionmoulding process does not consist of thermoplastics and waxes, but isformed by the molten low melting-point metallic phase acting as thebinder. The metal powder/binder mixture can be injected either directlyout of the extruder 4 into the mould 5 or, as shown in the drawing,first placed inside a cylinder 6 and then pressed into the cavity 8 ofthe mould 5 by means of a plunger 7.

In the following step V, a moulded part matching or substantiallymatching the final shape of the engine component is demoulded aftercooling and solidification, and can be machined with a low amount ofmetal-cutting in a further step VI. The low melting-point metallic phaseacting as the binder in the metal injection moulding process in step IVremains in the moulded part, meaning that unlike in conventional metalinjection moulding the moulded part created in the injection mouldingprocess does not have the binder removed.

In a subsequent step VII, the moulded part is subjected to a specificheat treatment matched to the two metallic phases, in this case iron andaluminum, in order to create a high-temperature resistant intermetallicphase. Since a compact (non-porous) moulded part is already availableafter demoulding, unlike in the known metal injection moulding processthat uses a thermoplastic binder, there is no hard-to-control shrinkageof the component during the heat treatment intended to create theintermetallic compound.

As a result of the previously described process steps I to VII, anengine component consisting of an intermetallic compound, beinghigh-temperature resistant and also low in weight due to the use oflightweight components is provided, which can be manufacturedcost-efficiently and with a comparatively low production effort in astructure of almost any complexity. Besides the material combination ofiron and aluminum mentioned above as an example, a plurality of otherhigh melting-point and low melting-point metallic phases, for exampletitanium and aluminum, can be used.

LIST OF REFERENCE NUMERALS

First hopper of 3 (Fe powder)

Second hopper of 3 (Al melt)

Extruder

Extruder screw

Mould

Cylinder

Plunger

Cavity of 5

What is claimed is:
 1. Method for near net shape manufacturing ofhigh-temperature resistant engine components of geometrically complexdesign consisting of an intermetallic phase, characterized in that atleast one low melting-point metallic phase in the molten state or in atemperature range near the molten state is mixed with at least one highmelting-point metallic phase provided as a metal powder, that themixture is mechanically treated, thereby heating it up and reducing itsviscosity, and that subsequently in an injection moulding process theengine component substantially matching the final contour is formed andafterwards subjected to a heat treatment for creating an intermetallicphase.
 2. Method in accordance with claim 1, characterized in thatmixing of the low melting-point phase and the high melting-point phaseis performed in an extruder under the effect of kneading and shearforces.
 3. in accordance with claim 1, characterized in that the metalpowder/ melt mixture is additionally heated by heating means.
 4. inaccordance with claim 1, characterized in that the engine componentdemoulded after solidification is subjected to a finish-machiningprocess before the heat treatment.